1. Field of the Invention
The present invention relates to insulated containers which comprise an insulated container and an insulated lid which covers the mouth of the insulated container, such as vacuum flasks, cooler boxes, ice boxes, insulated cups, insulated tableware, temperature maintaining lunch boxes, and the like. In particular, the present invention relates to an insulated container formed using a transparent material such as synthetic resin or glass, and having a double-walled structure with an insulating layer lying therein, and a manufacturing method therefore.
The present application is based on Japanese Patent Application No. Hei 10-161157, Japanese Patent Application No. Hei 11-60891, and Japanese Patent Application No. Hei 11-99380 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
In thermally insulated containers such as vacuum flasks, cooler boxes, ice boxes, insulated cups, insulated tableware, and temperature maintaining lunch boxes, conventionally, a metal double-walled container is used which has been made to have an insulating function by arranging a stainless steel inner container and a stainless steel outer container so that a space is formed therebetween, joining the mouths of these inner and outer containers to give a single body, and then vacuum-evacuating the above-mentioned space. In addition, in order to improve the insulating function further, in particular, for the purpose of preventing heat radiation, a layer of metallic plating such as copper or silver has been formed, or copper or aluminum foil has been arranged on the surface of the wall of the inner container or the outer container which face the above mentioned space. However, with these types of insulated containers, since the inner and outer containers are made from metal such as stainless steel, it is not possible to see the inside of the container from the side. In order to check the condition of the contents housed in the container, it is necessary to look through the opening. For this reason, due to the opening of the opening every time the contents of the container are checked, heat is lost or gained through the opening, and therefore there is the problem that despite having a temperature maintaining function as an intrinsically thermally insulated container, the intrinsic temperature maintaining property cannot maintained.
Because of this situation, for situations such as checking the amount of liquid held within the container, for example, liquid level gauges have been provided which are formed from a glass tube which is attached with one end connected to the bottom of the container and the other end connected to the upper end of the inside of the container. However, with this type of structure, since it is an insulated container, it is also necessary for this attached glass liquid gauge to be insulated. When the gauge is set inside of the insulation layer, additionally, it is necessary for processing to provide an air tight window in the stainless steel outer container in order to be able to see the gauge. For this reason, in this situation, not only are the number of necessary parts increased, but manufacture is made complex and manufacturing costs are increased.
In addition, there are double-walled containers of synthetic resin or glass which are formed by arranging inner and outer containers, made using synthetic resin or glass, leaving a space therebetween, and then joining them at their respective mouths to form a single body. In addition, various types of insulation layers can be formed. For the above mentioned synthetic resin containers, insulation layers are made by positioning solid insulation materials, forming an air layer within the space, or the like. For the above mentioned glass containers, an insulation layer is formed by vacuum evacuation of said space. With insulated containers having this type of structure, in order to prevent thermal radiation, metal foil is positioned on, or metal plating is applied to the surface of the walls facing the above mentioned space. As a result of this, despite the fact that the inner and outer containers are transparent, visibility of the inside of the container is blocked, and it is not possible to see the inside of the container. On the other hand, if the container is made in such a way that the inside can be seen, it is necessary to omit the arrangement of metal foil or plating for the above mentioned prevention of thermal radiation, and this is a problem because it runs counter to the goal of improving insulating efficiency.